The shape of a bird or airplane wing causes the air flowing over and under the wing to produce different pressures. The air pressure under the wing is higher than the air pressure over the wing. The two pressures push against each other (above and below the wing) with the higher pressure winning and pushing the wing up. These two videos explain it in greater detail.
Flight
The shape of a bird or airplane wing causes the air flowing over and under the wing to produce different pressures. The air pressure under the wing is higher than the air pressure over the wing. The two pressures push against each other (above and below the wing) with the higher pressure winning and pushing the wing up. These two videos explain it in greater detail.